The pictures below provides an overview of the changes in position of various tissues on the embryo's surface during gastrulation in Xenopus. These pictures are adapted directly from pictures hand-drawn by Dr. Ray Keller, Univ. of Virginia, and are based on his fate maps of superficial cells in Xenopus. Note the dramatic spreading of the light blue material (presumptive epidermis), and the convergence and extension of the dark blue material (presumptive neural ectoderm) as gastrulation proceeds. Also note that the yellow material (endoderm) becomes completely covered by ectodermal tissue by the end of gastrulation. The green material is material that will form part of the archenteron. The dorsal non-involuting marginal zone, which gives rise to the tissue of the neural plate during neurulation, undergoes convergence and extension, converging towards the dorsal side of the embryo (on the left here) and extending along the forming anterior-posterior axis.